1. Field of the Invention
The present invention relates to a process for preparing acrolein by the oxidation of propylene and more particularly, to the process for preparing acrolein in the presence of a solid catalyst having a core-shell structure represented in the formula 1,
[BinAaOx][(100-z)%EeFe1NigMomOy+z%SiO2]xe2x80x83xe2x80x83(1) 
wherein A is at least one element selected from the group consisting of boron, phosphorus, and molybdenum;
E is at least one element having the atomic valence of 2;
when m is 1, n is 0.001-3, a is 0-3, e is 0-3, f is 0.01-5, g is 0.1-5, and z is 0-90; and
x and y are numbers such that the valence requirements of the other elements for oxygen in the core and shell catalytic phase, respectively, are satisfied.
2. Description of the Prior Art
Acrolein has been widely used as a raw material in the synthesis of acylates and fine chemical products such as fibers, papers, paints, adhesives, and leathers. Further, demand of acrolein is continuously increased with the development of polymer related technologies and there are also trending to develop applications thereof in various fields.
Acrolein has been first synthesized by high temperature degradation of glycerin and further vapor-phase oxidation of acrolein gives acrylic acid. Since after, acetylene method using Ni as a catalyst, ethylene method using Pd as a catalyst, hydrolysis of acrylonitrile by using sulfuric acid and the like have been developed to synthesize acrolein. The most industrially useful and attractive method is by the oxidation of propylene due to its economic merit. On the other hand, the aldol condensation of formaldehyde and acetic acid has been extensively studied.
General process for preparing acrolein is by the oxidation of propylene in the presence of a mixed oxide catalyst having Bixe2x80x94Moxe2x80x94O system at about 400xc2x0 C. And further oxidation of acrolein is performed at about 300xc2x0 C. in the presence of an oxide catalyst having Moxe2x80x94Vxe2x80x94O system to produce acrylic acid.
In Korea, I.G company has introduced Nippon Shokubai process to prepare acrolein and acrylic acid and this process is divided into two stages. The first stage of process is to produce acrolein in the presence of a mixed oxide catalyst having Bixe2x80x94Moxe2x80x94Fexe2x80x94Coxe2x80x94O system at a reaction temperature of 325xc2x0 C. and a pressure of 2.5-3.0 atm and the second is to produce acrylic acid in the presence of a molybdate oxide catalyst at a reaction temperature of 270xc2x0 C. and a pressure of 2 atm. Total yield of the process to produce acrolein and acrylic acid is 81 to 85%.
Use of a catalyst in the oxidation of olefins brought an importance of selection of a catalyst, and results in extensive studies relating to such catalysts. Further, it has been developed not only in processes of reactions but also in compositions of catalyst and processes for preparing thereof. As a result, yield of producing acrylic acid by the oxidation is over 90%, and yield of producing acrylonitrile by ammoxidation is over 80% in plant.
Korean Patent No. 0247556, which is registered by the inventors of the present invention, discloses the use of a solid catalyst having core-shell structure in the preparation of acrylonitrile by ammoxidation of olefins. They have proved that said solid catalyst comprising a core catalyst phase containing Mo, Fe, Ni, and Si which is prepared by slurry technique, and a shell catalyst phase containing bismuth which is prepared by a impregnation technique using the core catalyst phase as a support, provides more excellent activities than conventional catalysts by examining their activities.
The present invention has been accomplished by obtaining the fact that use of the solid catalyst having a core-shell structure disclosed in Korea Patent No. 0247556 exhibits excellent activity in the oxidation of propylene to give acrolein.
Therefore, an object of the present invention is to provide a process for preparing acrolein at a high yield.
The present invention relates to a process for preparing acrolein by the oxidation of propylene and more particularly, to the process for preparing acrolein in the presence of a solid catalyst having core-shell structure represented in the formula 1,
[BinAaOx][(100-z)%EeFefNigMomOy+z%SiO2]xe2x80x83xe2x80x83(1) 
wherein A is at least one element selected from the group consisting of boron, phosphorus, and molybdenum;
E is at least one element having the atomic valence of 2;
when m is 1, n is 0.001-3, a is 0-3, e is 0-3, f is 0.01-5, g is 0.1-5, and z is 0-90; and
x and y are numbers such that the valence requirements of the other elements for oxygen in the core and shell catalytic phase, respectively, are satisfied.
The Detailed description of the present invention is given hereunder.
The present invention is characterized by use of a solid catalyst having a core-shell structure for preparing acrolein from propylene by the oxidation at a high yield.
According to Korea Patent No. 0247556, the activities of such a catalyst having the core-shell structure vary with compositions and ratios of each component comprised in the core phase and the shell phase, even the chemical composition of the catalyst is the same. The maximum activity of the solid catalyst is achieved when the core phase comprises [(100-z)%EeFefNigMomOy+z%SiO2] and the shell phase comprises [BinAaOx] by the synergy effect. Further, it affects manufacturing cost by using minimum content of expensive bismuth which is an essential component of the conventional catalyst.
This present invention is also characterized by a process for preparing acrolein at a high yield by the oxidation of propylene in the presence of said solid catalyst having a core-shell structure, and the oxidation condition is described in detail.
The reaction temperature of oxidation is in the range of 300 to 500xc2x0 C., preferably 350 to 400xc2x0 C. If the reaction temperature deviates from the range, it causes such problems in the conversion of propylene and selectivity to acrolein due to increase of un-reacted reactants or by-products. Preferred pressure of the reaction is in the range of 1 to 5 atm. If the pressure deviates from the range, the selectivity to / rapidly decreases. The reaction can be affected by the ratio of reactants. Preferred molar ratio of reactants (propylene/oxygen/nitrogen) is 1/1 to 20/1 to 20. The reaction can be also affected by the contact time and preferred contact time is in the range of 0.5 to 5 seconds.
The mechanism of the oxidation of propylene in the presence of the solid catalyst having a core-shell structure is described in detail hereunder.
In the catalyst having a core-shell structure, the core and shell catalytic phase functions independently and differently and the activity of the catalyst varies with the composition thereof and the ratio of each component comprised therein. According to the present invention, when the core phase comprises [(100-z)%EeFefNigMomOy+z%SiO2] and the shell phase comprises [BinAaOx], the maximum activity of the solid catalyst is achieved by the synergy effect.
The following examples illustrate various aspects of this invention but are not to be construed to limit the claims in any manner whatsoever.